Low energy consumption RF telemetry control for an implantable medical device

• US 6,456,887 B1
• Filed: 12/14/2000
• Issued: 09/24/2002
• Est. Priority Date: 12/14/2000
• Status: Expired due to Fees

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Haubrich, Gregory J., Dudding, Charles H.
• Primary Examiner(s): Schaetzle, Kennedy
• Application Number:
  US09/736,625
• Time in Patent Office: 649 Days
• Field of Search: 607/30, 607/32, 607/60, 607/31, 128/903, 340/573.1, 331/1.R, 455/343, 455/182.2
• US Class Current: 607/60
• CPC Class Codes: A61N 1/3727 characterised by the modulation technique
• CPC Class Codes: A61N 1/37276 characterised by means for reducing power consumption during telemetry

Abstract

In an implantable medical device, a frequency synthesizer employed in the RF transceiver of the IMD operating system functions in a PLL LOCK mode wherein the VCO frequency is governed by the PLL and an energy saving HOLD mode wherein the PLL is not operational and the VCO generated carrier frequency can drift over time. The PLL circuit is powered up and coupled with a control voltage input and the output of the VCO to develop a frequency control voltage stored by a capacitive loop filter during initial LOCK portions of both uplink and downlink telemetry transmission time periods. A frequency modulation (FM) input of the VCO receives data bit modulation voltages that modulates the carrier frequency during uplink transmission of patient data. During the HOLD portion of a downlink telemetry transmission, an AFC algorithm is enabled and derives a frequency correction value from the difference in frequency of the constant received carrier frequency and the drifting VCO generated carrier frequency, and the frequency correction value is applied to the VCO FM input to compensate for loop filter capacitor discharge of the control voltage causing the drift. The AFC algorithm derived frequency correction value is stored in memory and is also applied during the HOLD portion of an uplink telemetry transmission to the VCO FM input to compensate for loop filter capacitor discharge of the control voltage causing the drift. In addition, a recharge current is applied to the capacitive loop filter.

Claims

1. In a battery powered, implantable medical device (IMD) adapted to be implanted in a patient'"'"'s body to provide a therapy delivery and/or monitoring function, telemetry transceiver circuitry for uplink telemetry transmission of IMD developed patient data from the IMD during a predetermined uplink telemetry transmission time period and downlink telemetry reception of downlink telemetry data during a predetermined downlink telemetry transmission time period, said IMD further comprising:

a voltage-controlled oscillator (VCO) having a VCO voltage input for developing an FM telemetry carrier frequency at a VCO output dependent upon a control voltage applied to the VCO voltage input and a VCO frequency modulation (FM) input that receives a data bit modulation voltage that modulates the VCO generated carrier frequency during uplink transmission of patient data;

a phase-lock loop (PLL) circuit having a PLL input adapted to selectively receive the carrier frequency at the VCO output and to supply a control voltage to said capacitive loop filter a capacitive loop filter circuit that is coupled to the VCO voltage control input;

telemetry control means operable upon initiation of an uplink or downlink telemetry transmission for operating said VCO with said PLL circuit and said loop filter as a frequency synthesizer in a high battery energy consumption state for an initial LOCK portion of the uplink telemetry transmission time period to establish a frequency lock control voltage stored by said loop filter circuit and applied to said VCO voltage input to cause said VCO to generate a frequency locked carrier signal at said VCO output;

means for selectively de-coupling said PLL circuit from said VCO and applying patient data to said FM input during a subsequent HOLD portion of an uplink telemetry transmission time period; and

voltage hold means operable during the HOLD portion of the uplink telemetry transmission time period for establishing a frequency correction voltage at the VCO FM input which modulates the VCO generated carrier frequency in a manner that compensates for drift in the VCO generated carrier frequency to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

2. The IMD of claim 1, wherein said capacitive loop filter circuit voltage tends to dissipate over time at a predetermined rate as said loop filter capacitor discharges during said HOLD portion of said uplink telemetry transmission time period, and further comprising recharging means for recharging said loop filter capacitor to offset the discharge thereof.

3. The IMD of claim 2, further comprising:

means for storing a recharge current value derived from a leakage rate observed during testing of the capacitive loop filter during fabrication of the IMD in IMD memory; and

wherein;

said recharging means retrieves from IMD memory and uses said recharge current value it to develop and apply a recharge current value to said loop filter capacitor to recharge said loop filter capacitor.

4. The IMD of claim 1, further comprising:

automatic frequency control (AFC) means responsive to the difference between a received carrier frequency signal received from the remote medical device and the carrier frequency generated by the VCO during the HOLD portion of the downlink telemetry transmission time period for establishing an AFC correction value varying as a function of the difference between the received carrier frequency signal received from the remote medical device and the carrier frequency generated by the VCO; and

converting means for converting the AFC correction value to a frequency correction voltage and applying the frequency correction voltage to the FM input of said VCO during the HOLD portion of the downlink telemetry transmission time period to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable downlink telemetry reception of downlink telemetry data.

5. The IMD of claim 4, wherein said capacitive loop filter circuit voltage tends to dissipate over time at a predetermined rate as said loop filter capacitor discharges during said HOLD portion of said downlink telemetry transmission time period, and further comprising recharging means for recharging said loop filter capacitor to offset the discharge thereof.

6. The IMD of claim 5, further comprising:

means for storing a recharge current value derived from a leakage rate observed during testing of the capacitive loop filter during fabrication of the IMD in IMD memory; and

wherein;

said recharging means retrieves from IMD memory and uses said recharge current value to develop and apply a recharge current value to said loop filter capacitor to recharge said loop filter capacitor.

7. The IMD of claim 6, wherein said voltage hold means further comprises means responsive to the AFC correction value established by the AFC means during the HOLD portion of the downlink telemetry transmission time period and operable during the HOLD portion of the uplink telemetry transmission time period for establishing a frequency correction voltage at the VCO FM input which modulates the VCO generated carrier frequency in a manner that compensates for drift in the VCO generated carrier frequency to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

8. The IMD of claim 4, wherein said voltage hold means further comprises means responsive to the AFC correction value established by the AFC means during the HOLD portion of the downlink telemetry transmission time period and operable during the HOLD portion of the uplink telemetry transmission time period for establishing a frequency correction voltage at the VCO FM input which modulates the VCO generated carrier frequency in a manner that compensates for drift in the VCO generated carrier frequency to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

9. In a battery powered, implantable medical device (IMD) adapted to be implanted in a patient'"'"'s body to provide a therapy delivery and/or monitoring function, a method of providing uplink telemetry transmission of IMD developed patient data from the IMD during a predetermined uplink telemetry transmission time period and downlink telemetry reception of downlink telemetry data during a predetermined downlink telemetry transmission time period, said method further comprising the steps of:

within the IMD, providing a transceiver comprising a transmitter, a receiver, a voltage-controlled oscillator (VCO) having a voltage input and a frequency modulation (FM) input for developing an FM telemetry carrier frequency at a VCO output dependent upon a control voltage applied to the voltage input and an FM input signal applied to the FM input, and a phase-lock loop (PLL) circuit having a PLL input adapted to selectively receive the carrier frequency at the VCO output and to supply a control voltage to a capacitive loop filter circuit that is coupled to the VCO voltage input;

upon initiation of an uplink telemetry transmission, operating said VCO with said PLL circuit and said loop filter as a frequency synthesizer in a high battery energy consumption state for an initial LOCK portion of the uplink telemetry transmission time period to establish a frequency lock control voltage stored by said loop filter circuit and applied to said VCO voltage input to cause said VCO to generate a frequency locked carrier signal at said VCO output applied to said transmitter;

de-coupling said PLL circuit from said VCO and applying patient data to said FM input during a HOLD portion of the uplink telemetry transmission time period;

and

providing a frequency correction voltage to said FM input during the HOLD portion of the uplink telemetry transmission time that is sufficient to maintain a carrier frequency generated by said VCO at said VCO output within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

10. The method of claim 9, wherein said capacitive loop filter circuit voltage tends to dissipate over time at a predetermined rate as a loop filter capacitor discharges during said uplink telemetry transmission time period, and the providing step further comprises recharging said capacitor to offset the discharge thereof.

11. The method of claim 10, wherein the providing step further comprises the steps of:

storing a recharge current value derived from a leakage rate observed during testing of the capacitive loop filter during fabrication of the IMD in IMD memory; and

retrieving said recharge current value from IMD memory and applying a recharge current to said loop filter capacitor.

12. The method of claim 11, further comprising the steps operable upon reception of a downlink telemetry transmission of a downlink telemetry data modulated carrier frequency signal by said receiver of:

operating said VCO coupled with said PLL circuit and said loop filter as a frequency synthesizer in a high battery energy consumption state for an initial LOCK portion of the downlink telemetry transmission time period to establish a frequency lock control voltage stored by said loop filter circuit and applied to said VCO voltage input to cause said VCO to generate a frequency locked carrier signal at said VCO output;

de-coupling said PLL circuit from said VCO during a subsequent HOLD portion of the downlink telemetry transmission time period;

providing a received carrier signal upon receipt of the downlink telemetry data modulated carrier frequency signal;

generating a frequency correction voltage from the difference in frequency between the received carrier frequency signal and the carrier frequency generated by the VCO during the HOLD portion of the downlink telemetry transmission time period; and

applying the frequency correction voltage to the FM input of said VCO during the HOLD portion of the downlink telemetry transmission to provide automatic frequency control of the carrier frequency generated by the VCO.

13. The method of claim 12, wherein the generating step further comprises the steps of:

applying an automatic frequency control (AFC) algorithm to the frequency difference between the received carrier frequency signal received from the remote medical device and the carrier frequency generated by the VCO during the HOLD portion of the downlink telemetry transmission time period to establish an AFC correction value varying as a function of the difference between the received carrier frequency signal received from the remote medical device and the carrier frequency generated by the VCO; and

converting the AFC correction value to a frequency correction voltage value.

14. The method of claim 13, further comprising the steps of:

establishing a frequency correction voltage from the AFC correction value derived during the HOLD portion of the downlink telemetry transmission time period; and

applying the frequency correction voltage to the FM input of said VCO during the HOLD portion of an uplink telemetry transmission time period to modulate the VCO generated carrier frequency in a manner that compensates for drift in the VCO generated carrier frequency to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

15. The method of claim 9, further comprising the steps operable upon reception of a downlink telemetry transmission of a downlink telemetry data modulated carrier frequency signal by said receiver of:

operating said VCO coupled with said PLL circuit and said loop filter as a frequency synthesizer in a high battery energy consumption state for an initial LOCK portion of the downlink telemetry transmission time period to establish a frequency lock control voltage stored by said loop filter circuit and applied to said VCO voltage input to cause said VCO to generate a frequency locked carrier signal at said VCO output;

de-coupling said PLL circuit from said VCO during a subsequent HOLD portion of the downlink telemetry transmission time period;

providing a received carrier signal upon receipt of the downlink telemetry data modulated carrier frequency signal;

generating a frequency correction voltage from the difference in frequency between the received carrier frequency signal and the carrier frequency generated by the VCO during the HOLD portion of the downlink telemetry transmission time period; and

applying the frequency correction voltage to the FM input of said VCO during the HOLD portion of the downlink telemetry transmission to provide automatic frequency control of the carrier frequency generated by the VCO.

16. The method of claim 15, wherein the generating step further comprises the steps of:

applying an automatic frequency control (AFC) algorithm to the frequency difference between the received carrier frequency signal received from the remote medical device and the carrier frequency generated by the VCO during the HOLD portion of the downlink telemetry transmission time period to establish an AFC correction value varying as a function of the difference between the received carrier frequency signal received from the remote medical device and the carrier frequency generated by the VCO; and

converting the AFC correction value to a frequency correction voltage value.

17. The method of claim 16, further comprising the steps of:

establishing a frequency correction voltage from the AFC correction value derived during the HOLD portion of the downlink telemetry transmission time period; and

applying the frequency correction voltage to the FM input of said VCO during the HOLD portion of an uplink telemetry transmission time period to modulate the VCO generated carrier frequency in a manner that compensates for drift in the VCO generated carrier frequency to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

18. A method of conserving energy during uplink and downlink telemetry transmissions of data between a remote device and an implantable medical device (IMD) employing frequency modulation of a predetermined carrier frequency, comprising the steps of:

providing, in the IMD, a phase-lock loop (PLL) circuit having a capacitive loop filter connected to a control voltage input of a voltage-controlled oscillator (VCO), an output of said VCO providing a carrier signal as a function of a control voltage of the capacitive loop filter during uplink and downlink telemetry transmissions;

during an initial LOCK portion of an uplink or downlink telemetry transmission, operating said PLL circuit, said VCO, and said loop filter as a voltage synthesizer in a phase-lock process long enough to charge a capacitor of the capacitive loop filter to a control voltage sufficient to cause said VCO to generate a carrier frequency within a selected acceptable frequency deviation tolerance from the predetermined carrier frequency;

during a subsequent HOLD portion of an uplink or downlink telemetry transmission applying the control voltage to the VCO; and

during the HOLD portion of a downlink telemetry transmission;

generating a frequency correction voltage from the difference in frequency between the received carrier frequency signal and the carrier frequency generated by the VCO; and

applying the frequency correction voltage to the FM input of said VCO to provide automatic frequency control of the carrier frequency generated by the VCO.

19. The method of claim 18, further comprising the step of providing a frequency correction voltage to said FM input during the HOLD portion of the uplink telemetry transmission time that is sufficient to maintain a carrier frequency generated by said VCO at said VCO output within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

20. The method of claim 19, wherein said capacitive loop filter circuit voltage tends to dissipate over time at a predetermined rate as a loop filter capacitor discharges during uplink and downlink telemetry transmission time periods, and the providing step further comprises recharging said capacitor to offset the discharge thereof during the uplink and downlink telemetry transmission time periods.

21. The method of claim 20, wherein the providing step further comprises the steps of:

storing a recharge current value derived from a leakage rate observed during testing of the capacitive loop filter during fabrication of the IMD in IMD memory; and

retrieving said recharge current value from IMD memory and applying a recharge current to said loop filter capacitor.

22. In a battery powered, implantable medical device (IMD) adapted to be implanted in a patient'"'"'s body to provide a therapy delivery and/or monitoring function, telemetry transceiver circuitry for uplink telemetry transmission of IMD developed patient data from the IMD during a predetermined uplink telemetry transmission time period and downlink telemetry reception of programming and interrogation commands during a predetermined downlink telemetry transmission time period, said IMD further comprising:

a voltage-controlled oscillator (VCO) having a voltage input and a frequency modulation (FM) input for developing an FM telemetry carrier frequency at a VCO output dependent upon a control voltage applied to the voltage input and an FM input signal applied to the FM input;

a capacitive loop filter circuit coupled to the VCO voltage control input for providing a control voltage, said capacitive loop filter circuit comprising a capacitor;

a phase-lock loop (PLL) circuit having a PLL input adapted to selectively receive the carrier frequency at the VCO output and to supply a control voltage to a capacitive loop filter circuit that is coupled to the VCO voltage input;

uplink telemetry control means operable upon initiation of an uplink telemetry transmission or reception of a downlink telemetry transmission for operating said VCO with said PLL circuit and said loop filter as a frequency synthesizer in a high battery energy consumption state for a LOCK portion of the uplink telemetry transmission time period to establish a frequency lock control voltage stored by said loop filter circuit and applied to said VCO voltage input to cause said VCO to generate a frequency locked carrier signal at said VCO output;

means operable during a HOLD portion of an uplink or downlink telemetry transmission for applying the control voltage to the VCO;

means operable during the HOLD portion of an uplink telemetry transmission for providing a frequency hold control voltage to the loop filter circuit that is sufficient to maintain a frequency hold carrier frequency generated by said VCO at said VCO output within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data; and

means operable during the HOLD portion of a downlink telemetry transmission for;

generating a frequency correction voltage from the difference in frequency between the received carrier frequency signal and the carrier frequency generated by the VCO; and

applying the frequency correction voltage to the FM input of said VCO to provide automatic frequency control of the carrier frequency generated by the VCO.

23. The IMD of claim 22 further comprising:

voltage hold means coupled with said loop filter circuit and operable during the HOLD portion of the uplink telemetry transmission time period for establishing a frequency correction voltage at the VCO FM input which modulates the VCO generated carrier frequency in a manner that compensates for drift in the VCO generated carrier frequency to maintain the VCO generated carrier frequency within an acceptable frequency deviation tolerance enabling reliable uplink telemetry transmission of patient data.

24. The IMD of claim 22, wherein said capacitive loop filter circuit voltage tends to dissipate over time at a predetermined rate as said loop filter capacitor discharges during said HOLD portion of said uplink telemetry transmission time period, and further comprising recharging means for recharging said loop filter capacitor to offset the discharge thereof.

25. The IMD of claim 24, further comprising:

means for storing a recharge current value derived from a leakage rate observed during testing of the capacitive loop filter during fabrication of the IMD in IMD memory; and

wherein;

said recharging means retrieves from IMD memory and uses said recharge current value to develop and apply a recharge current value to said loop filter capacitor to recharge said loop filter capacitor.